Rapid and long‐lasting efficacy of high‐dose ambroxol therapy for neuronopathic Gaucher disease: A case report and literature review

Abstract Gaucher disease (GD) is a lysosomal storage disorder caused by a deficiency in the GBA1‐encoded enzyme, β‐glucocerebrosidase. Enzyme replacement therapy is ineffective for neuronopathic Gaucher disease (nGD). High‐dose ambroxol has been administered as an alternative treatment for a group of patients with nGD. However, little is known about the clinical indication and the long‐term outcome of patients after ambroxol therapy. We herein report a case of a female patient who presented with a progressive disease of GD type 2 from 11 months of age and had the pathogenic variants of p.L483P (formerly defined as p.L444P) and p.R502H (p.R463H) in GBA1. A combined treatment of imiglucerase with ambroxol started improving the patient's motor activity in 1 week, while it kept the long‐lasting effect of preventing the deteriorating phenotype for 30 months. A literature review identified 40 patients with nGD, who had received high‐dose ambroxol therapy. More than 65% of these patients favorably responded to the molecular chaperone therapy, irrespective of p.L483P homozygous, heterozygous or the other genotypes. These results highlight the long‐lasting effect of ambroxol‐based chaperone therapy for patients with an expanding spectrum of mutations in GBA1.


| INTRODUCTION
Gaucher disease (GD) is an autosomal recessive lysosomal storage disease caused by pathogenic variations in the GBA1 gene (Suner & Delhommeau, 2022).Resulting deficits in the activity of glucocerebrosidase (GCase) lead to the accumulation of the substrates, glucocerebroside and glucosylsphingosine in tissue macrophages (Suner & Delhommeau, 2022).Affected individuals present with hepatosplenomegaly, skeletal deformity and hematopoietic cell dysfunctions.Patients without neurological symptoms receive the diagnosis of type 1 GD (GD1), and this type of disease is more frequently found in Caucasian than in Asian ancestries (Tajima et al., 2009).
GD type 2 (GD2) and type 3 (GD3) are collectively designated as neuronopathic GD (nGD) (Tajima et al., 2009) that predominantly affects the central nervous system (CNS) of patients (Narita et al., 2016).The clinical expressions of GD2 develop in infants and young children and lead to a rapid progression, distinctively from those of GD3 as the later-onset and chronic form of the disease (Narita et al., 2016).In contrast to the dominant prevalence rate of GD1 in Western countries, 60% of patients in Asian countries are classified into those with nGD (Tajima et al., 2009).Enzyme replacement therapy (ERT; Charrow & Scott, 2015;Suner & Delhommeau, 2022) and substrate reduction therapy (Cox et al., 2015;Lukina et al., 2014;Mistry et al., 2015) are promising procedures to ameliorate the systemic symptoms in patients with GD1.However, these treatment effects are known to be limited in patients with nGD.The reason is primarily related to the fact that neither recombinant GCase nor glucosylceramide synthase inhibitors penetrate the blood-brain barrier (BBB) efficiently (Ivanova et al., 2021).
A chemical screening has identified ambroxol to be a molecular chaperone that rescues the hydrolyzing activity of mutant GCase (Maegawa et al., 2009).Because ambroxol is considered to pass the BBB, it may serve as an alternative medicine for patients with nGD.It remains to be investigated, however, whether the chaperone therapy might be also effective for patients carrying other mutations in GBA1 (Ivanova et al., 2021).In this report, we present a pediatric patient with GD2 who showed a favorable neurodevelopmental response to the high-dose ambroxol administration with ERT during follow-up for more than 2 years (30 months).

| CASE REPORT
A 15-month-old girl was transferred to our hospital by ambulance for acutely exacerbating stridor and cyanosis of unidentified causes.The patient was born to unrelated, healthy parents after an uneventful pregnancy and delivery.The optional newborn screening for lysosomal diseases was not performed at the birthplace in Japan.She was noticed to have bilateral esotropia in her early infancy and was referred to an ophthalmologist at her 4month health check-up.Recurrent dysphagia and cyanosis started from the age of 11 months.Hypotonia, growth arrest, and psychomotor retardation were noticed and treated at a previous hospital from the age 12 months.
A literature review identified 40 patients with nGD, who had received high-dose ambroxol therapy.More than 65% of these patients favorably responded to the molecular chaperone therapy, irrespective of p.L483P homozygous, heterozygous or the other genotypes.These results highlight the long-lasting effect of ambroxol-based chaperone therapy for patients with an expanding spectrum of mutations in GBA1.

K E Y W O R D S
ambroxol, chaperone, Gaucher disease, genotype, glucocerebrosidase, therapy admission, opisthotonic postures recurrently emerged with or without sensory stimulations.Repeated cranial MRI determined no degenerative lesions in the CNS (Figure 1b).
After the start of imiglucerase and ambroxol therapy, the patient began to roll over in 1 week and to sit unaided in 2 weeks (Figure 1c).During this period, spasticity and opisthotonus disappeared.The platelet counts increased to 150-200 × 10 9 /L within 2 months of treatment.Because prolonged dysphagia and laryngospasm hampered to achieve a safe and successful extubation, tracheostomy was performed on day 9 after admission.She was Hepatosplenomegaly discharged from our hospital on day 48 after Given the chronic dyspepsia, the dose of imiglucerase was increased to 80 units/kg every other week from age 19 months.She then underwent laryngotracheal separation to control recurrent airway infections at the age of 27 months.Esophageal hiatal hernia was surgically repaired at age 3 years and 6 months.Serial monitoring of molecular markers supported the efficacy of the treatments.Increased ACE levels declined from 76.2 U/L on admission to 50.5 U/L in 1 month and to 20.5 U/L at the latest evaluation (age 2 years and 6 months; Figure 1c).Similarly, tartrate-resistant acid phosphatase 5b (TRACP-5b) was initially as high as 7150 mU/dL (120-420) but declined to 1770 mU/dL during the treatment course.In addition, serum glucosylsphingosine (Lyso-Gb1) showed a decreasing trend from 720.7 ng/ mL (health control; 3.8) at the beginning of treatment to 129.7 ng/mL at 5 months after the start of treatment.
No serious adverse were observed during the follow-up period.
At the present age of 3 9 months, the patient walks independently, and her cognitive function has reached 12-16 months of developmental age.The healthrelated quality of life score (PEDsQL™ 4.0 Generic Core Scales; Varni et al., 1999) showed marked improvement from before treatment (score: 29.3) to 2 years after starting ambroxol therapy (score: 76.0), reflecting a good quality of life with treatment.

| DISCUSSION
We have first demonstrated the response of a young girl with GD2 to more than 30 months of ambroxol and imiglucerase therapy.This patient showed a favorable neurological development without adverse events during the follow-up period.The literature review of 40 patients including the present one determined >65% of response rate to ambroxol and ERT irrespective of the genotype of nGD.Considering both the neuroprotective and less deleterious effects of ambroxol, the treatment protocol might be worth proposing for broader populations of patients with nGD.Five Japanese patients with nGD have been shown to favorably respond to high-dose ambroxol (Narita et al., 2016).In these patients, the chaperone therapy improved myoclonic seizures and ocular apraxia.Consistently, their laboratory data showed increased lymphocyte GCase activity and decreased glucosylsphingosine levels in the cerebrospinal fluid (Narita et al., 2016).In agreement with this perspective, rapid escalation in the administration dose of ambroxol is known to produce faster and better outcomes (Kim et al., 2020).More recently, a longitudinal study showed that ambroxol was safely and effectively used for siblings with GD3 (one from age 5 to 12 years; the other from age 7 weeks to 7 years; Ramadza et al., 2021).Thus, in the era of expanding newborn screening, ambroxol will serve as a preemptive therapy for infants at risk of developing nGD.
Ambroxol acts as a molecular chaperone that improves the decreased activity of mutant GCase (Maegawa et al., 2009).Besides this well-defined mechanism, recent studies have suggested that eliglustat and ambroxol improved autophagy-lysosome dynamics and mitochondrial functions, thereby enhancing the GCase activity in vitro (Ivanova et al., 2021).Of note, mutations in GBA1 are associated with Parkinson disease (PD) in adults, and ambroxol has been effectively used for these patients (Istaiti et al., 2021;Mullin et al., 2020).The emerging molecular models may rationalize the clinical findings that ambroxol showed therapeutic effects on symptoms of PD without GBA1 mutations (Mullin et al., 2020).These results suggest that ambroxol may not only rescue the enzymatic activity of mutant GCase, but also recover misfolded proteins in various tissues.
As in previous reports, our patient was treated with ERT and ambroxol, and her improvement in blood data and neurological symptoms could be attributed to the combination of these agents.On the other hand, the clinical course of our patient suggests that ambroxol does not necessarily improve brainstem dysfunction leading to laryngospasm and dysphagia.Based on these findings, we speculate that the brainstem might be more vulnerable to lysosomal dysfunctions than neurons in the cerebral cortex.Thus, respiratory failure, cardiac arrhythmia and other signs of dysautonomia must be observed carefully during the follow-up period.
In conclusion, the immediate start of ambroxol was effective for a young child with the unique combination of mutant alleles (p.L483P and p.R502H) among previously reported cases with nGD.Expanding newborn screening is expected to provide further evidence for the rapid and long-lasting efficacy of chaperone therapy for infants and young children with a variety of genotypes.

T A B L E 1
The response rate of patients who received ambroxol therapy.

F
Clinical profiles and the treatment course of the present case.(a) May-Grunwald-Giemsa staining for Gaucher cells (arrows) in the bone-marrow smear.Scale, 10 μm.(b) Sagittal T1-weighted (left) and axial fluid-attenuated inversion recovery (FLAIR, middle) image on day 24 of admission.No parenchymal lesion was detected in the FLAIR image at 3 months after discharge (right).(c) Clinical course of the patient.Treatments are shown at the top.Neurological findings and laboratory data are depicted in the middle and lower schemes, respectively.ACE, angiotensin-converting enzyme; TRACP-5b, Tartrate-Resistant Acid Phosphatase 5b.

F
I G U R E 2 A mutational landscape of 40 patients who received ambroxol therapy for neuronopathic Gaucher disease.(a) The gene structure of GBA1 located at chromosome 1q22.Shaded boxes represent the 11 protein-coding exons spanning the 6.8-kb region in the negative strand of the human genome.The left-to-right direction corresponds to that of transcription.Annotations indicate 23 pathogenic variants identified in patients with neuronopathic Gaucher disease.Horizontal bars represent the domain structure of GCase.Red: mutant alleles identified in the present patient.All the 40 patients having these variants were reported to receive the ambroxol treatment.(b) Pie chart indicates the number and frequency (%) of mutant alleles among 80 alleles identified in the 40 patients (panel a).-, unidentified variant.(c) A stereographic structure of GCase (UniProt: A0A068F658).The location of amino acid residues harboring nGD-associated variants is schematically shown.